There are few catalysts that are known to be capable of copolymerizing ethylene and conjugated dienes (e.g., isoprene) using a coordination-insertion mechanism under industrially relevant conditions. The introduction of unsaturated carbon-carbon bonds into a polyolefin is of interest because this serves as, inter alia, a route to produce vulcanized and/or functionalized polymers. These polymers have numerous potential applications, including those that require adhesion to and compatability with other materials. One potential use for such materials is as a component in tire sidewalls and treads, where compatability and co-curability with other tire materials (e.g., natural rubber, styrene-butadiene rubber, and cis-polybutadiene) is desirable.
Polysisoprene homopolymers and polyethylene homopolymers were prepared by Doring, Kretschmer, and Kempe in the European Journal of Inorganic Chemistry 2010, pp. 2853-2860 using various aminopyridinate complexes; however, ethylene-isoprene copolymers are not disclosed.
Ethylene isoprene copolymers are also relatively rare. U.S. Pat. No. 6,288,191 B1 discloses the production of ethylene-isoprene random copolymers using a cyclopentadientyl-based titanium catalyst system, where the copolymers have high 1,4 isoprene isomer content.
J. Am. Chem. Soc., 2009, 131, pp. 13870-13882, discloses the production of ethylene-isoprene random copolymers using a cyclopentadienyl-based scandium catalyst system.
Catal. Sci. Technology, 2012, 2, pp. 2090-2098, discloses the attempted production of ethylene-isoprene copolymer using a cyclopentadienyl-titanium catalyst system where the copolymer has a melt peak at or above 133° C.
Eur. Polym. J., 1997, 33, 4, pp. 447-451, discloses the production of ethylene-isoprene copolymer using a zirconocene catalyst system, where the copolymer contains low content of isoprene and a high melting point of 119° C.
Polymer, 2008, 49, pp. 2039-2045, discloses the production of ethylene-isoprene copolymer using a neodymocene catalyst system where the copolymer has high isoprene content.
J. Polym. Sci. A, 2010, 48, pp. 4200-4206, discloses copolymerization of ethylene with isoprene promoted by titanium complexes containing a tetradentate [OSSO]-type bis(phenolato) ligand, where the copolymers have high 1,4 isoprene isomer content.
Other references of interest include: Macromol Chem Phys., 2001, 202, pp. 2485-2488; Macromolecules, 2002, 35, 1143-1145; JP-B-48-56775; US 2014/0018493; US 2014/0005327; and US 2013/0197174.
There is still a need in the art for new and improved catalysts capable of producing ethylene copolymers with conjugated dienes, including isoprene. Catalysts capable of producing high molecular weight copolymer under industrially relevant conditions are desired. Highly productive catalysts are desired. Catalysts capable of producing ethylene-isoprene copolymer with low levels of 1,4-isoprene insertions relative to 3,4-insertions are desired.
It is, therefore, an object of the present invention to provide a process to produce ethylene conjugated diene copolymers with excellent molecular weight (Mw) and polydispersity (Mw/Mn) using a family of Group 3 transition metal (preferably Sc or Y) catalysts at industrially relevant temperatures and pressures.